Preparation and optimization of oxygenated gasolines

ABSTRACT

A process for controlling the composition of an xBOB so that the xBOB will yield an oxygenate-containing gasoline which precisely meets desired specifications when mixed with the desired amount of oxygenate. The process involves blending a plurality of blendstocks to produce an xBOB, withdrawing a sample of the xBOB, obtaining spectroscopic measurements for the sample, applying mathematical models that were based on correlation of xBOB spectra to associated oxygenate-containing gasoline properties, to predict laboratory analysis results for oxygenate-containing gasoline properties, and using the analysis results to control and optimize the blending process.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a continuation application which claims the benefitof and priority to U.S. application Ser. No. 12/277,454 filed Nov. 25,2008, entitled “Preparation and Optimization of Oxygenated Gasolines”,which is hereby incorporated by reference in its entirety.

BACKGROUND OF THE INVENTION

1. Field of the Invention

This invention relates to the preparation of oxygenate-containingfinished gasoline, wherein the finished gasoline is manufactured bymixing an oxygenate-free substantially hydrocarbon blend, also hereinreferred to as “xBOB”, with a known, constant quantity and constantcomposition of one or more oxygenates. More particularly, the inventionprovides an improved blend control process for xBOB manufacture tomaintain pre-determined properties of the oxygenate-containing finishedgasoline from such a process.

2. Description of the Prior Art

Gasoline is comprised of a complex mixture of volatile hydrocarbonswhich are suitable for use as a fuel in a spark-ignition internalcombustion engine, and it typically boils over a temperature range ofabout 80° to about 437° F. Although gasoline can consist of a singleblendstock, such as the product from a refinery alkylation unit, it isusually comprised of a blend of several blendstocks. The blending ofgasoline is a complex process, which typically involves the combinationof from as few as three or four to as many as twelve or more differentblendstocks to meet regulatory requirements and such otherspecifications as the manufacturer may select. Optimization of thisblending process must take into account a plurality of characteristicsof both the blendstocks and the resulting gasoline. Among others, suchcharacteristics can include cost and various measurements of volatility,octane, boiling point characteristics, and chemical composition.

It is conventional practice in the industry to blend gasoline usingblendstock ratios which are determined by mathematical algorithms alsoknown as blending equations. Such blending equations are well known inthe refining industry, and are either developed or tailored by eachrefiner and refinery for use in connection with available blendstocks.Blending equations typically relate the properties of a gasoline blendto the quantity of each blendstock in the blend and also to either themeasured or anticipated properties of each blendstock in the blend.

Although hydrocarbons usually represent a major component of gasoline,it has been found that certain oxygen containing organic compounds canbe advantageously included as gasoline components. These oxygencontaining organic compounds are referred to as “oxygenate” or“oxygenates,” and are useful as components in gasoline because they areusually of high octane and can be a more economical source of gasolineoctane than a high octane hydrocarbon blending component such asalkylate or reformate. As used herein, the term “oxygenate” includesboth the singular “oxygenate” and the plural “oxygenates.” Currentgovernment regulations in the U.S. limits the oxygen content of gasolineto about 3.8 weight percent, based on elemental oxygen, and alsorequires that reformulated gasolines contain at least 1.5 weight percentof oxygenate or 10 volume percent denatured fuel ethanol, as inaccordance with ASTM D4806-08b or the most current ASTM version.Oxygenates which have received substantial attention as gasolineblending agents include, but are not limited to, methanol, ethanol,tertiary-butyl alcohol, methyl tertiary-butyl ether, ethyltertiary-butyl ether, and methyl tertiary-amyl ether. However, ethanolhas become one of the most widely used oxygenates.

Oxygenate, if desired, usually is not blended into a gasoline at orwithin a refinery because oxygenates can be water soluble. As aconsequence of this water solubility, an oxygenate-containing gasolinecan undergo undesirable changes if an oxygenate-containing gasolinecomes in contact with water during transport through any portion of adistribution system, which may include pipelines, stationary storagetanks, rail cars, tanker trucks, barges, ships and the like. Forexample, an oxygenate-containing gasoline can absorb or dissolve waterwhich will then be present as an undesirable contaminant in thegasoline. Alternatively, water can extract oxygenate from the gasoline,thereby changing the chemical composition of the gasoline and negativelyaffecting the specifications of the gasoline. In order to avoid, as muchas possible, any adverse effects from water, oxygenate-containingfinished gasoline usually is manufactured by a multi-step processwherein the oxygenate is incorporated into the gasoline at a point whichis near the end of the distribution system.

More specifically, gasoline which contains oxygenates generally ismanufactured by producing an unfinished and substantially hydrocarbonblendstock, xBOB, at a refinery, transporting the xBOB to a productterminal in the geographic area where the finished gasoline is to bedistributed, and mixing the xBOB with the desired amount of oxygenate atthe product terminal. The combination of the xBOB with an oxygenateyields an oxygenate-containing finished gasoline which meets allregulations and specifications for sale.

As used herein, the substantially hydrocarbon blendstock, can be, andusually is, called an “xBOB” (Blendstock for Oxygenate Blending) whenthe blendstock is destined to be combined with a predetermined quantityand quality oxygenate to produce finished gasoline. xBOB is not aconsistent blend and can vary with refinery or blending operationsExamples of xBOB include, but are not limited to RBOB (reformulatedblendstock for oxygenate blending), CBOB (conventional reformulatedblendstock for oxygenate blending), CARBOB (California reformulatedblendstock for oxygenate blending), Chicago BOB (Chicago RBOB or Chicagoreformulated blendstock for oxygenate blending), Arizona RBOB, andAlbuquerque RBOB. There can be a variety of other names for “BOB”gasolines.

Oxygenate-free finished gasoline can be manufactured within a refineryto very precisely fit the final US government specifications becauseanalytical data for the product can be used to control the blendingprocess. As a consequence, manufacturing costs are kept to a minimum byminimizing the amount of more costly refinery blendstocks in the blend.

When an xBOB is manufactured at a refinery, the xBOB properties aretypically measured and controlled to meet intermediate specificationsthat differ from the finished gasoline. The intermediate specificationsare developed to ensure that xBOB produced with a relatively wide rangeof compositions will always meet finished gasoline specifications afterit is mixed with a predetermined quantity and quality oxygenate. As aresult of targeting intermediate specifications, the xBOB and oxygenatemixture on average exceed the finished gasoline specifications. Forexample, an advanced closed loop feedback control system that is able toproduce an xBOB to meet an intermediate octane target to within 0.01octane points will often yield a finished octane after addition ofethanol that varies from 0.1 to 0.4 octane points above the minimumfinished gasoline specification. Producing xBOB with lower precision inthe meeting finished gasoline specifications after mixing the xBOB withoxygenate requires a more expensive average refinery blendstock andincreases manufacturing costs.

SUMMARY OF THE INVENTION

Most oxygenate-containing finished gasoline is manufactured by a twostep process which comprises manufacturing an oxygenate-freesubstantially hydrocarbon blend, or xBOB, in a refinery, transportingthe xBOB to a product terminal in the geographic area where theoxygenate-containing finished gasoline is to be distributed, andpreparing the oxygenate-containing finished gasoline at the productterminal by mixing the xBOB with a predetermined quality and quantity ofoxygenate. The octane, volatility, and other properties of the resultingmixture are dependent not only on the xBOB to oxygenate ratio, but onthe composition of the xBOB. As a result, it is difficult to produce anoxygenate-containing finished gasoline by this multi-step procedurewhich has the precise octane, volatility, and other desired propertiesto meet finished gasoline specifications.

We have determined that the composition of an xBOB can be controlled toyield an oxygenate-containing finished gasoline which precisely meetsdesired specifications when mixed with a known, constant quantity andconstant composition of oxygenate by a modification of the blendingprocess that is used to produce an xBOB. The modification involves useof chemometric models that predict the oxygenate-containing finishedgasoline properties from spectroscopic data for the xBOB. These modelscan be applied via on-line spectroscopic analysis of a product streamfor continuous property monitoring. A closed-loop control system makesnecessary adjustments to automatically blend the components in order tomaintain oxygenate-containing finished gasoline properties based onmodel predictions. The models are developed through a process whichinvolves withdrawing a sample of the xBOB, acquisition of spectroscopicdata, mixing the xBOB with a known quality and quantity of oxygenate,determining one or more physical properties of the mixture usingstandard laboratory methods, and using the analysis result for a seriesof xBOB stream samples to create a model that correlates spectroscopicdata for the xBOB stream to the laboratory results for theoxygenate-containing finished gasoline.

One embodiment of the invention is a process for preparing an xBOB whichcan be converted to an oxygenate-containing finished gasoline of desiredspecifications by mixing the xBOB with a constant quantity and qualityof oxygenate, wherein a plurality of blendstocks are mixed to yield thexBOB, and wherein said process comprises: (a) using chemometric modelsto predict the oxygenate-containing finished gasoline properties fromspectroscopic data for the xBOB; (b) applying said chemometric models toan xBOB product stream using either on-line or off-line spectroscopicanalysis to continuously monitor the gasoline properties, (c) usingeither a manual control system or a closed loop control system toautomatically adjust the ratio of blendstock streams to maintainoxygenate-containing finished gasoline properties based on modelpredictions.

Another embodiment of the invention comprises a process for preparing acalibration model for the prediction of properties for anoxygenate-containing finished gasoline of desired specifications fromspectroscopic data for an xBOB wherein the process comprises:

-   -   (a) collecting an xBOB stream sample;    -   (b) analyzing the xBOB stream sample by one or more        spectroscopic methods to produce an analyzed xBOB product        spectrum;    -   (c) transmitting the spectrum of the analyzed xBOB product to a        conversion device to mathematically correct or enhance the        spectrum to create a corrected spectrum;    -   (d) adding a fixed, known quantity of a pre-determined oxygenate        composition to said analyzed xBOB product to produce an        associated oxygenate-containing gasoline;    -   (e) performing laboratory tests on said associated        oxygenate-containing gasoline to determine laboratory results        for one or more chemical or physical properties; and    -   (f) correlating the spectra from a series of xBOB streams to the        laboratory results for the associated oxygenate-containing        gasoline products to produce a calibration model. Another        embodiment of the invention further comprises the additional        step of:        -   (h) transmitting the predicted results from the model to a            control system, wherein said control system can modify the            ratio of blendstocks in the xBOB stream to produce an xBOB            stream that when combined with a fixed, known quantity of a            pre-determined oxygenate composition will produce an            associated oxygenate-containing finished gasoline.

BRIEF DESCRIPTION OF THE DRAWING

The drawing, FIG. 1, is a schematic representation of a gasolineblending system utilizing one embodiment of the present invention.

DETAILED DESCRIPTION

As used herein, the term “finished gasoline” refers to a gasolineproduct that meets all required regulations and specifications. However,“finished gasoline” may not contain federally mandated requiredadditives, such as detergents; “finished gasoline” can be used as fuelfor retail use. The term “oxygenate-containing finished gasoline” refersto gasoline products containing one or more oxygenates that meets allrequired regulations. Again, “oxygenate-containing finished gasoline”may not contain federally mandated required additives, such asdetergents; “oxygenate-containing finished gasoline” can be used as fuelfor retail use.

Any oxygenate or mixture of oxygenates can be used in the practice ofthis invention. However, monohydric aliphatic alcohols are usually mosttypical of oxygenates which are currently employed commercially in themanufacture of oxygenate-containing finished gasoline. Alcohols whichcontain from 1 to about 10 carbon atoms can be conveniently used.Desirable alcohols will contain from 1 to 5 carbon atoms, and preferredalcohols will contain from 1 to 4 carbon atoms. For example, the alcoholof oxygenate-containing finished gasolines of this invention can becomprised of at least one compound which is selected from the groupconsisting of methanol, ethanol, 1-propanol, 2-propanol, 1-butanol,2-butanol, 2-methyl-l-propanol, 2-methyl-2-propanol, 1-pentanol,2-pentanol, 2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol,3-methyl-2-butanol and mixtures thereof. Methanol and ethanol are highlysatisfactory alcohols for use in the practice of this invention.

In the practice of this invention, the oxygenate-containing finishedgasoline can be prepared by mixing any desired amount of oxygenate withthe xBOB. For example, the oxygenate-containing finished gasoline cancontain 1%, 10%, 50%, 99% or any other desired amount of oxygenate.However, it will be appreciated that the invention will typically bemost useful in manufacturing oxygenate-containing finished gasoline fordistribution to motorists.

To prepare the calibration model useful in this invention for theprediction of properties of an oxygenate-containing finished gasolinehaving desired specifications from spectroscopic data, one or more xBOBstreams can be collected. The xBOB stream can be obtained from anysource, but exemplary sources include, but are not limited to,commercial or non-commercial streams, such as refinery streams orlaboratory-generated streams. Preferably, the xBOB stream(s) iscollected from a refinery. Conventional blendstocks which can be used inthe manufacture of an xBOB in accordance with the invention include, butare not limited to, catalytically cracked naphtha, coker naphtha,reformate, virgin naphtha, isomerate, alkylate, raffinate, naturalgasoline, polymer gasoline, pyrolysis gasoline, pentane, butane, xylene,toluene, and the like, and mixtures thereof. However, it should be notedthat blendstock nomenclature varies from refinery to refinery, and thenames listed here are only exemplary in that other names can be used foridentical or similar blendstocks.

The xBOB stream then can be analyzed by one or more spectroscopicmethods to produce one or more analyzed xBOB product spectrum/spectra.Any type of spectroscopic analysis can be used and exemplaryspectroscopic analyses methods are selected from the group consisting ofRaman spectroscopy, nuclear magnetic resonance spectroscopy, infrared(IR) spectroscopy, such as, for example, near IR, medium IR, and one ormore thereof. Preferably, for ease of use, near infrared spectroscopy isthe preferred spectroscopic analytical method. The acquired spectra areperformed at the wavelength, wavelengths, or wavelength range ofinterest and the spectrum can be at one or more wavelengths. Thespectrum of the analyzed xBOB stream then is transmitted to a conversiondevice to mathematically process to correct or enhance the spectrum tocreate and store one or more corrected spectrum/spectra. Exemplarymathematical processing includes, but is not limited to, firstderivative, second derivative, baseline correction, no correction, andcombinations of two or more thereof.

The analyzed xBOB stream then is combined, or mixed, with a fixed, knownquantity of a pre-determined oxygenate composition to produce anassociated oxygenate-containing finished gasoline. Laboratory analysesare performed on this associated oxygenate-containing finished gasolineto determine one or more physical properties. These properties caninclude, but are not limited to, one or more of research octane, motoroctane, distillation properties (such as T10, T20, T50, T90), and alsoproperties such as evaporated volume percent (E200, E300), olefincontent, paraffins content, aromatics content, and benzene content. Theresults of these laboratory analyses, “laboratory results,” are pairedwith and saved with the associated corrected spectra analyses from thexBOB streams. Preferably, 20 xBOB samples associated with theoxygenate-finished gasoline are collected, more preferably 100 runs.Most preferably, for best mathematical correlation, 200, or even more,xBOB samples associated with the oxygenate-finished gasoline arecollected.

Then, a mathematical model is created using standard modeling methods tocorrelate the corrected spectra for a series of xBOB steams to thelaboratory results for the associated oxygenate-containing finishedgasoline products. Any type of mathematical modeling equations orprograms can be used. Exemplary modeling programs include, but are notlimited to, chemometric methods such as partial least squares (PLS),multiple linear regression (MLR), principle component regression (PCR),multivariate regression analyses, multivariate statistical analyses, andcombinations of two or more thereof. Application of these modelingprograms, can be used to correlate the xBOB spectra with the desiredproperties of the oxygenate-containing finished gasoline such that, themodel property prediction will, in the long run, and under normal andcorrect operation of the test methods, be at least statisticallyequivalent to the results of a different operator working in a differentlaboratory testing identical material. Alternatively, application ofthese modeling programs can be used to correlate the xBOB spectra withthe desired properties of the oxygenate-containing finished gasolinesuch that, the model property prediction will be within six (6) standarddeviation units at 95% of the time, preferably within three (3) standarddeviation units, and most preferably within two (2) standard deviationunits at 95% of the time for best optimized correlations.

Another embodiment of the invention further comprises the additionalstep of transmitting the predicted results from the model to a controlsystem, wherein said control system can adjust the ratio of refineryblendstocks that are mixed to produce an xBOB stream that when combinedwith a fixed, known quantity of a pre-determined oxygenate compositionwill produce an associated oxygenate-containing finished gasoline.

THEORETICAL EXAMPLE

One embodiment of the present invention is schematically illustrated inFIG. 1. FIG. 1 illustrates mixing a plurality of blendstocks to make anxBOB stream, mixing the xBOB stream with a constant quantity andcomposition oxygenate to prepare an oxygenate-finished gasoline. Withreference to FIG. 1, tanks 2, 4, 6, 8, 10, and 12 contain gasolineblending stocks, such as, for example, reformates, isomerates,alkylates, and others. Each of these blending stocks has its ownproperties as well as a price and value. For example, reformate andalkylate are both high in octane number (a property of gasoline), butare relatively expensive blending stocks. Each of the tanks has anautomatic control valve 14, 16, 18, 20, 22, and 24 which controls theflow of the particular blending stock from the tank into common header26 and thence delivered to mixing tank, pipeline, or transportationvehicle 28. Mixing tank, pipeline or transportation vehicle 28 containsxBOB. Control valves 14, 16, 18, 20, 22, and 24 also can be aproportioning pump. Tanks 2, 4, 6, 8, 10, and 12 and control valves 14,16, 18, 20, 22, and 24 are merely exemplary of a blending system; therecan be more or less tanks and control valves. Pump 30 if needed, can beused to move the blended gasoline through “on-line” analyzer 32 whichobtains spectroscopic measurements of side-stream 40 at the wavelength,wavelengths, wavelength range of interest. The spectroscopicmeasurements, or signals, from analyzer 32 are transmitted tomathematical conversion device 34 which mathematically preprocesses thespectroscopic measurements or signals. Preprocessing examples include,but are not limited to, first derivative, second derivative, baselinecorrection, no processing, and others. The mathematical model, describedabove, is applied to the preprocessed signal for the xBOB productdelivered to mixing tank, pipeline, or transportation vehicle 28 topredict the properties of the oxygenate-containing finished gasoline.The predicted results of the oxygenate-containing finished gasoline arefed to control system 36 which manages closed-loop control of theblending process. Optional display device 38 can display both the targetproperties and the measured properties at all times. The output fromcontrol system 34 is fed to each control valve 14, 16, 18, 20, 22, and24, and can control the relative flow of each of the gasoline blendingcomponents 2, 4, 6, 8, 10, and 12 into blending tank, pipeline, ortransportation vehicle 28. Various adjustments can be made for hold-upin the tank, line fill, etc. Alternately, the functions of themathematical conversion device 34 can also be performed by controlsystem 36. The resulting gasoline can be controlled to target propertylimits within a specified tolerance.

In a variation, an operator can read the control system 34 output ofgasoline properties on display device 38 and manually or mechanicallycontrol and optimize the blending process.

Numerical Ranges

The present description uses numerical ranges to quantify certainparameters relating to the invention. It should be understood that whennumerical ranges are provided, such ranges are to be construed asproviding literal support for claim limitations that only recite thelower value of the range as well as claims limitation that only recitethe upper value of the range. For example, a disclosed numerical rangeof 10 to 100 provides literal support for a claim reciting “greater than10” (with no upper bounds) and a claim reciting “less than 100” (with nolower bounds).

Definitions

As used herein, the terms “comprising,” “comprises,” and “comprise” areopen-ended transition terms used to transition from a subject recitedbefore the term to one or more elements recited after the term, wherethe element or elements listed after the transition term are notnecessarily the only elements that make up the subject.

As used herein, the terms “including,” “includes,” and “include” havethe same open-ended meaning as “comprising,” “comprises,” and“comprise.”

As used herein, the terms “having,” “has,” and “have” have the sameopen-ended meaning as “comprising,” “comprises,” and “comprise.”

As used herein, the terms “containing,” “contains,” and “contain” havethe same open-ended meaning as “comprising,” “comprises,” and“comprise.”

As used herein, the terms “a,” “an,” “the,” and “said” mean one or more.

As used herein, the term “and/or,” when used in a list of two or moreitems, means that any one of the listed items can be employed by itselfor any combination of two or more of the listed items can be employed.For example, if a composition is described as containing components A,B, and/or C, the composition can contain A alone; B alone; C alone; Aand B in combination; A and C in combination; B and C in combination; orA, B, and C in combination.

Claims Not Limited to the Disclosed Embodiments

The preferred forms of the invention described above are to be used asillustration only, and should not be used in a limiting sense tointerpret the scope of the present invention. Obvious modifications tothe exemplary embodiments, set forth above, could be readily made bythose skilled in the art without departing from the spirit of thepresent invention.

The inventors hereby state their intent to rely on the Doctrine ofEquivalents to determine and assess the reasonably fair scope of thepresent invention as pertains to any apparatus not materially departingfrom but outside the literal scope of the invention as set forth in thefollowing claims.

1-10. (canceled)
 11. A method to control an xBOB output stream, whichcomprises: (a) spectroscopically analyzing an xBOB stream to producespectrum of said analyzed xBOB product; (b) correcting said spectrummathematically to produce a corrected spectra; (c) applying acalibration model to said corrected spectra; (d) obtaining predictedlaboratory results from said calibration model; (e) transferring saidpredicted laboratory results to a control system; (f) modifying theratio of blendstock components of said xBOB stream based on said resultsto produce an xBOB output stream that when said xBOB stream is combinedwith a fixed, known quantity of a predetermined oxygenate will producean oxygenate-containing gasoline product having preset physicalproperties.
 12. A method in accordance with claim 11 wherein said xBOBcomprises mixtures of hydrocarbons selected form the group consisting ofcatalytically cracked naphtha, coker naphtha, reformate, virgin naphtha,isomerate, alkylate, raffinate, natural gasoline, polymer gasoline,pyrolysis gasoline, pentane, butane, xylene, toluene, and mixturesthereof.
 13. A method in accordance with claim 11 wherein spectroscopicmethods are selected from the group consisting of nuclear magneticresonance spectroscopy, Raman spectroscopy, infrared (IR) spectroscopy,and one or more thereof.
 14. A method in accordance with claim 11wherein said spectroscopic method is near infrared spectroscopy.
 15. Amethod in accordance with claim 11 wherein said oxygenate is amonohydric aliphatic alcohol having from about one to about 10 carbonatoms per molecule.
 16. A method in accordance with claim 11 whereinsaid monohydric oxygenate is selected from the group consisting ofmethanol, ethanol, 1-propanol, 2-propanol, 1-butanol, 2-butanol,2-methyl-1-propanol, 2-methyl-2-propanol, 1-pentanol, 2-pentanol,2-methyl-1-butanol, 3-methyl-1-butanol, 2-methyl-2-butanol,3-methyl-2-butanol and mixtures of two or more thereof.
 17. A method inaccordance with claim 11 wherein said oxygenate is selected from thegroup consisting of methanol and ethanol.
 18. A method in accordancewith claim 11 wherein said physical properties are selected from thegroup consisting of research octane, motor octane, T10 distillation, T20distillation, T50 distillation, T90 distillation, E200, E300, olefincontent, paraffins content, aromatics content, and benzene content. 19.A method in accordance with claim 11 wherein said correlation process isa chemometric method selected from the group consisting of partial leastsquares (PLS), multiple linear regression (MLR), principle componentregression (PCR), multivariate regression analyses, and multivariatestatistical analyses.
 20. A method in accordance with claim 11 whereinpredicted results are transmitted to a control system, wherein saidcontrol system can modify the ratio of blendstock components of the xBOBstream to produce an xBOB stream that when combined with a fixed, knownquantity of a pre-determined oxygenate composition will produce anassociated oxygenate-containing gasoline.